As semiconductor processing techniques push critical dimensions ever smaller, there are continuing challenges in forming adequate contacts with substrate node locations. For example, it is desirable in most instances to form diffusion regions to have a very shallow elevational thickness within a substrate. Yet, the act of establishing electrical connection with diffusion regions can diminish their size. Such typically happens where a silicide material is used to form an electrical contact to a diffusion region. This occurs because silicon is typically consumed by refractory metals when forming contact to silicon in the form of a silicide. As diffusion region thicknesses shrink, less silicon is available for consumption by the refractory metal. In some instances, an entire diffusion region can be consumed if too much refractory metal is reacted with the silicon, thus destroying the circuitry.
One solution to this problem would be to provide very thin refractory metal layers over diffusion regions with which electrical communication is desired. This approach, however, can lead to problems associated with the structural integrity of the ultimately-formed silicide layer. Specifically, silicide layers have grain sizes which are usually within known ranges. As an example, titanium silicide can have grain sizes from between 200 and 400 Angstroms. Accordingly, where very thin layers of titanium, e.g. 50 Angstroms, are formed over a silicon surface, the resulting silicide will attempt to, and effectively form grain sizes between 200 and 400 Angstroms. As the titanium layer is insufficiently thick to produce grains of this size and maintain complete coverage of the underlying silicon, what can occur is formation 200 Angstrom to 400 Angstroms grains which in essence can result in less than all of the exposed silicon being covered with titanium silicide.
This invention arose out of concerns associated with improving the methods by which electrical communication is established with substrate node locations. In particular, the invention arose out of concerns associated with shallow junction contacts where opening critical dimensions are less than or equal to 0.15 micron.